One of the major concerns about possible future bioterrorism attacks involving anthrax is that terrorist entities may easily develop B. anthracis strains resistant to many, if not all, currently recommended antibiotics. Our company has identified a promising class of synthetic compounds, pyridinium thio ethers (PTEs) that display strong bactericidal activity against a variety of Gram-positive bacteria, including B. anthracis. Some PTE compounds are active even against Bacillus spores. PTE compounds display little toxicity towards human cells in vitro, and are highly promising from the drug development standpoint: they are water-soluble, retain activity in the presence of human serum and are readily amenable to chemical modification and lead optimization efforts. Most importantly, it appears very difficult, if not impossible, to select Gram positive bacteria resistant to this class of compounds, which addresses the major shortcoming of the existing antibiotics as anti-anthrax drugs. Based on our preliminary data, we propose to develop PTE compounds as a narrow spectrum antibiotic for the post-exposure treatment of inhalation anthrax. In this proposal we seek funding for further biological characterization, chemical improvement and preclinical development of PTEs. The following specific aims will be pursued: AIM 1, Chemical improvement of PTE compounds for activity against B. anthracis, including synthesis of a diverse chemical library of PTEs and a QSAR-based iterative lead optimization; AIM2, Evaluation of in vitro activity of synthesized PTEs against B. anthracis, selection for resistance, and analysis of their toxicity to human cells; AIM 3, Determination of the biological mechanism of action of PTEs using genetic and biochemical approaches; AIM 4, In vivo anti-anthrax efficacy studies in a murine inhalational challenge model, including development of an oral formulation, acute toxicity tests, and preliminary pharmacokinetics; AIM 5, Pre-clinical (Pre-IND) drug development studies, including toxicity and pharmacokinetic studies with GLP material direc.